Abstract. This application requests an opportunity for a promising diversity candidate to expand his field of investigation to take on a new question regarding the role of CD39 activity in cardiovascular disease. 1. Research Plan Our current R01 R01HL127442, Ectonucleotidases in ischemic heart disease, studies the impact of CD39 activity on macrophages and fibroblast on post-myocardial infarction healing (see specific aims of parent grant in italics below). This application for a Diversity Training Supplement for Roman Covarrubias, PhD will provide a novel training opportunity while expanding upon the fundamental studies of the role of CD39 in monocyte and macrophage biology. The new direction will test the hypothesis that CD39 on monocytes impacts cell phenotype and may serve both as a prognostic marker of inflammation and a potential therapeutic target for novel treatment of cardiovascular disease. Parent Grant Specific Aims (extracted from R01): SPECIFIC AIMS: Over 1 million people per year suffer an acute myocardial infarction (MI) in the United States. Optimal cardiac repair requires controlled inflammatory and fibrotic responses. Inadequate cardiac healing can result in fatal cardiac rupture; aberrant fibrosis can lead to debilitating heart failure. Current treatments that target cardiac repair are limited. There is a critical need to understand novel pathways that modulate cardiac repair and to develop new therapies to prevent heart failure. Acute MI results in an initial release of nucleotides by dying cells. However, nucleotide release by activated inflammatory cells and fibroblasts is equally important. Extracellular ATP (eATP) can activate macrophages (Ms) and cardiac fibroblasts (CFs) through both paracrine and autocrine purinergic receptor signaling pathways (P2X and P2Y) to produce proinflammatory and profibrotic mediators. The hydrolysis of eATP to adenosine is accomplished through the sequential actions of the ectonucleotidases CD39 and CD73. Adenosine is purported to evoke anti-inflammatory and anti-fibrotic responses via P1 purinergic receptor activation. Therefore, the CD39/CD73 pathway is an important regulatory scale that balances inflammation and fibrosis. CD39 is the rate-limiting step in this metabolic pathway, as such, we have focused on understanding it's impact on cardiovascular pathology. Our prior R21 funded work dissected the molecular and cellular pathways by which increased CD39 activity reduces arterial thrombosis and myocardial damage following ischemia-reperfusion injury. Our long-term goal is to understand the role of ectonucleotidase activity on cardiovascular disease. The impact of CD39 activity on regulating cardiac repair after MI is not known. Therefore, the objective of this application is to understand the cellular and molecular mechanisms by which CD39 activity modulates post-MI repair and fibrosis. Our hypothesis is that regulated cell-specific expression of CD39 is necessary to resolve the inflammatory and fibrotic responses post-MI. The rationale for this research stems from our preliminary data that demonstrate that knockout of CD39 activity exacerbates cardiac fibrosis post-MI. To determine downstream targets responsible for this finding, we have focused on the role CD39 on macrophages and cardiac fibroblasts. Based, in part, on our preliminary data demonstrating dynamic changes in the expression and activity of CD39 on macrophages and cardiac fibroblasts, we hypothesize that upregulation of CD39 on macrophages and fibroblasts, serves as a molecular extinguisher, terminating nucleotide-mediated purinergic signals that promote inflammation and fibrosis in the infarcted heart. To test our hypothesis, we will explore distinct but related aims. Aim 1: To determine whether CD39 up-regulation is a protective mechanism that constrains autocrine ATP- driven inflammation, preventing exaggerated macrophage responses, and protecting from adverse post-MI fibrosis. Aim 2: To dissect the purinergic pathways involved in CD39-mediated restraint of TGF-?1 activation of cardiac fibroblasts and determine the role of CD39 upregulation in modulating fibroblast function and regulating cardiac repair following MI. Secondary Aim: To determine the impact of CD39 expression on extracellular matrix remodeling. The outcomes of these studies will reveal the fundamental pathways by which CD39 regulates post-MI myocardial repair and could allow novel therapeutic approaches not only to treat fibrotic disorders of the heart, but also of the skin, lungs, bone marrow, liver, or kidneys, thereby providing an important translational impact.